The present invention relates to mixed signal analog and digital circuits, and in particular, to circuits and methods for calibrating analog and digital circuits.
Electronic signal processing typically involves two different types of signals. Traditionally, electronic circuits processed signals as continuous waveforms, which are commonly referred to as analog signals. Accordingly, such circuits are referred to as analog circuits. As technology progressed, electronic circuits emerged where information was efficiently processed using digital signals, which are signals that only have discrete values representing, for example, zero (0) and one (1). Such circuits are referred to as digital circuits, digital processors, or digital signal processors, for example. However, the real world is an analog domain. Accordingly, for digital signal processing to be useful, it is often necessary to convert analog signals into to digital signals and convert digital signals into analog signals. Examples of systems that may use both analog and digital processing include wireless communications systems, control systems, or audio or video systems, for example.
Digital-to-analog converters (“DACs”) and analog-to-digital converters (“ADCs”) reside at the boundary between analog and digital domains. ADC circuits allow information represented by analog signals to flow into the digital domain for high speed, accurate, and cost effective digital processing. Once processed, DAC circuits allow the information to flow back into the analog domain for use in the real world. At the analog/digital boundary, analog circuits and digital circuits may be tightly coupled in operation and functionality. Conversion systems may integrate both types of circuits to perform the conversion task. Accordingly, these circuits are often call “mixed signal” or “hybrid” circuits because the circuits include both analog and digital features and components.
It is typically desirable to perform the conversion process with as much accuracy as possible. However, the analog circuitry in a conversion system may include components that vary across manufacturing processes. As a specific example, many analog circuits may include time constants implemented using capacitors and resistors that may exhibit an overall tolerance of up to 30% or more. However, a tolerance of just a few percentage may be required for the circuit to operate properly within the conversion system. In such cases, errors in the analog system can propagate and magnify as signals flow from the analog domain into the digital domain. Typically, the requirements on overall system accuracy are such that uncorrected manufacturing variations in the analog domain can render the system inoperable.
Traditional approaches for improving the accuracy of circuits are typically limited to one domain or the other. For example, existing approaches for improving analog circuit accuracy often include trimming or calibration techniques that focus on the specific values of particular components in the analog circuit. Digital domain accuracy is typically addressed by increasing the number of bits used to represent a signal and by various digital signal processing techniques.